Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 229 PM EDT Thu Oct 17 2019 Valid Oct 17/1200 UTC thru Oct 21/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Record Deep Surface Low in Northeast ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Very strong agreement exists with record deep cyclone in the Northeast, only the 00z CMC slightly shifts the center of the surface low toward the enhancing triple point over the St. Lawrence wobbling it further west. Each of the other guidance shows the strong triple point but still retains the older occluded center as dominant lifting through the Seaway. The CMC rotates back to the consensus after 30hrs, so a given the otherwise super strong consensus through the remaining mass fields, a general model blend is supported at above average confidence. Deep latitudinal Western trof progressing into the Plains by Fri...spurring Northern Plains surface low by late Thurs/Fri and Southern Plains surface low late Fri/Sat ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Models continue to show solid agreement for the initial height-falls/trof crossing the West today and developing a northern Plains surface wave that lifts northeast into Canada. The deep latitude trof, will also spur a secondary surface wave across the Southern Plains that will elongate/shear along the frontal zone as it drops south and the bulk of driving energy lifts north. As the northern portion of the wave crosses Central Canada, the trailing trof across the Great Lakes shows some mild mid-level difference, based mainly on typical slow break down of the ECMWF/CMC vs. the faster break down in the UKMET/GFS. This is not much of importance to the sensible weather across the Great Lakes, so a general model blend can be supported at above average confidence. NW-SE elongated shortwave entering Pac NW Sat, curling into compact developing closed low in lee of Central Rockies by Sun afternoon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 20.00z 12z NAM/ECMWF/CMC blend thereafter Confidence: Average 19z update: The 12z ECMWF/CMC both trended a bit slower emerging into the Central High Plains, putting further distance in timing and evolution to a more compact closed low with the 12z GFS and even the 12z NAM. The 12z UKMET also further slowed, and in doing so shifted south with the track/development of the wave as well. So will continue with the initial preference including the slowing trend with a 12z NAM/ECMWF/CMC blend after 20.00z, though confidence is reduced slightly to average after 20.00z. ---Prior Discussion--- In the wake of the initial height-falls (see section above), the mid to upper level flow is fairly flat and very strong across the Pacific. The nose of the approaching jet will help to spur a strong shortwave that is fairly flat initially entering the Pacific NW by Sat. Guidance is in strong agreement in placement/timing of this feature, but as the system crosses into the Western CONUS and starts to amplify (mainly the upstream jet buckles with a strong 150+ kt speed max along the SW periphery of the wave. As it crosses the Central Rockies, timing issues start to occur as the 12z GFS jet rounds the base of the trof allowing for faster vortex roll-up into the Central Plains by Sunday afternoon, spurring a deepening surface cyclone. The remaining guidance and ensembles (including a bulk of the GEFS members) are slower, with the UKMET uncharacteristically slow, perhaps too slow within the otherwise tighter ensemble members. As such after 20.00z, a 12z NAM and 00z ECMWF/CMC blend is preferred at slightly above average confidence (prior, a general model blend is sufficient). Potential Tropical Cyclone Sixteen ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Please refer to 15z NHC forecast Best Proxy: 12z GFS/UKMET up to 18.18z; 12z GFS/UKMET/ECMWF thereafter 19z update: The 12z ECMWF shows a bit more reflection of the initial surface wave emerging from the Central Gulf, but still has the greatest hybrid look through the vertical depth of the cyclone than the GFS/UKMET. While the ECMWF remains on the western side of the guidance, a blend in position of the ECMWF with the 12z GFS and 12z UKMET (which remained fairly consistent, perhaps a shade stronger) will be the closest proxy to the official NHC track/intensity starting a bit earlier around 18.18z...though a GFS/UKMET blend remains better in line prior to 18.18z. ---Prior Discussion--- Most of the guidance has finally come to consensus with the northern closed low across TX in terms of placement, depth, and shape to have better confidence in this portion of the stream. The tropical/subtropical stream is still a bit elongated and highly dependent on convective enhancement to the mass fields, so there remains moderate spread. The 12z GFS and 00z UKMET are well timed to the official NHC forecast even early in the forecast process but still on the southeast side of the official track. The 00z ECMWF shows stronger/tighter binary interaction between the northern and tropical streams deepening the surface wave very near the mouth of the MS River by 19.00z which is NW of the track. After 19.00z, the official forecast remains dominantly near the GFS/UKMET with some increasing weighting toward the ECWMF especially as the wave reaches NC/East Coast at 21.00z. The 12z NAM remains weak and slow, and CMC is also weak and well south of the track to not blend either. So, initially the best proxy to the 15z NHC forecast is a 06z GFS/00z UKMET blend up to 19.06z, then incorporate increasing influence/percentage to the 00z ECMWF after 19.06z. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina